This sort of advertising is important and has been used throughout the years by many bands, the beatles for example used their brand image to sell more merchandise and also to build popularity and become more mainstream (not that they needed it!)

Merchandise that includes the band's brand can usually be found on the band's website so that they can sell more. Bands are increasingly selling their merchandise online for ease of access to the public, also because distributors in more recent times have become able to sell to places all over the world. This allows fans who cannot go to see the artist in person because they live abroad.
Merchandise can also be sold when the bands are touring, usually at larger gigs where arena's are built with stands set up to sell whatever is there.
Branding is important because fans can instantly recognise a band's logo or image that is on the merchandise, branding can be widespread across all of the band, behind the stage, on the drum set, basically wherever the band choose to have it. One key example of this is Greenday with their logo of a hand holding a heart-shaped grenade, this image is used in their music videos as well as being on t-shirts and on their album cover.